Question

Сократите дробь
$\frac{a {}^{2} - a - 12 }{ 16 - {a}^{2} }$
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Answer 1

$\frac{a^2-a-12}{16-a^2}=\frac{a^2-4a+3a-12}{-(a^2-16)}=\frac{a(a-4)+3(a-4)}{-(a-4)(a+4)}=\\\\-\frac{(a-4)(a+3)}{(a-4)(a+4)}=-\frac{a+3}{a+4}$